Method of manufacturing CMOS devices by the implantation of N- and P-type cluster ions

ABSTRACT

A method of manufacturing a semiconductor device is described, wherein clusters of N- and P-type dopants are implanted to form the transistor structures in CMOS devices. For example, As 4 H x   +  clusters and either B 10 H x   −  or B 10 H x   +  clusters are used as sources of As and B doping, respectively, during the implants. An ion implantation system is described for the implantation of cluster ions into semiconductor substrates for semiconductor device manufacturing. A method of producing higher-order cluster ions of As, P, and B is presented, and a novel electron-impact ion source is described which favors the formation of cluster ions of both positive and negative charge states. The use of cluster ion implantation, and even more so the implantation of negative cluster ions, can significantly reduce or eliminate wafer charging, thus increasing device yields.  
     A method of manufacturing a semiconductor device is further described, comprising the steps of: providing a supply of dopant atoms or molecules into an ionization chamber, combining the dopant atoms or molecules into clusters containing a plurality of dopant atoms, ionizing the dopant clusters into dopant cluster ions, extracting and accelerating the dopant cluster ions with an electric field, selecting the desired cluster ion by mass analysis, modifying the final implant energy of the cluster ion through post-analysis ion optics, and implanting the dopant cluster ions into a semiconductor substrate. In general, dopant clusters contain n dopant atoms where n can be 2, 3, 4 or any integer number. This method provides the advantages of increasing the dopant dose rate to n times the implantation current with an equivalent per dopant atom energy of 1/n times the cluster implantation energy. This is an effective method for making shallow transistor junctions, where it is desired to implant with a low energy per dopant atom.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is a continuation-in-part of commonlyowned copending U.S. patent application Ser. No. ______, filed on Sep.16, 2002, entitled Electron Beam Ion Source With IntegralLow-Temperature Vaporizer, by Thomas N, Horsky, which is a continuationof U.S. patent application Ser. No. 09/736,097, filed on Dec. 13, 2000,now U.S. Pat. No. 6,452,338. This patent application also claimspriority of commonly owned copending U.S. provisional patent applicationserial No. 60/391,847, filed on Jun. 26, 2002, entitled Doping by theImplantation of Cluster Ions; and commonly owned copending U.S.provisional patent application serial No. 60/392,271, filed on Jun. 26,2002, entitled Cluster Beam Ion Implantation Using Negative Ions.

[0002] The following patent applications, herein incorporated byreference, are also related to the present application: PCT Application,Serial No. PCT/US00/33786, filed Dec. 13, 2000, entitled “IonImplantation Ion Source, System and Method”; PCT Application Serial No.PCT/US01/18822, filed Jun. 12, 2001, entitled “Ion Implantation withHigh Brightness, Low Emittance Ion Source, Acceleration-DecelerationTransport System and Improved Ion Source Construction”; and PCTApplication Serial No. PCT/US02/03258, filed Feb. 5, 2002, entitled,“Ion Source for Ion Implantation”; U.S. patent application Ser. No.10/183,768, filed Jun. 26, 2002, entitled “Electron Impact Ion Source”.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to an ion implantation system and amethod of semiconductor manufacturing which implants ion beams formedfrom clusters of the N-type dopant cluster ions, such as As₄H_(x)+ andP-type dopant cluster ions, such as B₁₀H_(x) ⁻.

[0005] 2. Description of the Prior Art

[0006] The fabrication of semiconductor devices involves, in part, theintroduction of impurities into the semiconductor substrate to formdoped regions. The impurity elements are selected to bond appropriatelywith the semiconductor material to create an electrical carrier andchange the electrical conductivity of the semiconductor material. Theelectrical carrier can either be an electron (generated by N-typedopants) or a hole (generated by P-type dopants). The concentration ofintroduced dopant impurities determines the electrical conductivity ofthe resultant region. Many such N- and P-type impurity regions must becreated to form transistor structures, isolation structures and othersuch electronic structures, which collectively function as asemiconductor device.

[0007] The conventional method of introducing dopants into asemiconductor substrate is by ion implantation. In ion implantation, afeed material containing the desired element is introduced into an ionsource and energy is introduced to ionize the feed material, creatingions which contain the dopant element (for example, the elements ⁷⁵As,¹¹B, ¹¹⁵In, ³¹P, or ¹²¹Sb. An accelerating electric field is provided toextract and accelerate the typically positively-charged ions, thuscreating an ion beam. Then, mass analysis is used to select the speciesto be implanted, as is known in the art, and the ion beam is directed ata semiconductor substrate. The accelerating electric field gives theions kinetic energy, which allows the ions to penetrate into the target.The energy and mass of the ions determine their depth of penetrationinto the target, with higher energy and/or lower mass ions allowingdeeper penetration into the target due to their greater velocity. Theion implantation system is constructed to carefully control the criticalvariables in the implantation process, such as the ion beam energy, ionbeam mass, ion beam current (electrical charge per unit time), and iondose at the target (total number of ions per unit area that penetrateinto the target). Further, beam angular divergence (the variation in theangles at which the ions strike the substrate) and beam spatialuniformity and extent must also be controlled in order to preservesemiconductor device yields.

[0008] It has recently been recognized, for example, by Kishimoto etal., “A High-Current Negative-Ion Implanter and its Application forNanocrystal Fabrication in Insulators”, IEEE Proceedings of the XII^(th)International Conference on Ion Implantation Technology, Kyoto, Japan,pp. 342-345 (1999), and Ishikawa et al., “Negative-Ion ImplantationTechnique”, Nuclear Instruments and Methods in Physics Research B 96,pp. 7-12 (1995), and others in the field that implanting negative ionsoffers advantages over implanting positive ions. One very importantadvantage of negative ion implantation is to reduce the ionimplantation-induced surface charging of modern processor and memorydevices during the manufacturing process. In general, the implantationof high currents (on the order of 1 mA or greater) of positive ionscreates a positive potential on the gate oxides and other components ofthe semiconductor device which can easily exceed gate oxide damagethresholds. When a positive ion impacts the surface of a semiconductordevice, it not only deposits a net positive charge, but liberatessecondary electrons at the same time, multiplying the charging effect.Thus, equipment vendors of ion implantation systems have developedsophisticated charge control devices, so-called electron flood guns, tointroduce low-energy electrons into the positively-charged ion beam andonto the surface of the device wafers during the implantation process.Such electron flood systems introduce additional variables into themanufacturing process, and cannot completely eliminate yield losses dueto surface charging. As semiconductor devices become smaller andsmaller, transistor operating voltages and gate oxide thicknesses becomesmaller as well, reducing the damage thresholds in semiconductor devicemanufacturing, further reducing yield. Hence, negative ion implantationpotentially offers a substantial improvement in yield over conventionalpositive ion implantation for many leading-edge processes.Unfortunately, this technology is not yet commercially available, andindeed negative ion implantation has not to the author's knowledge beenused to fabricate integrated circuits, even in research and development.

[0009] Prior art negative ion sources have relied upon so-callednegative affinity sputter targets. A heavy inert gas, such as xenon, isfed into a plasma source which creates Xe⁺ ions. Once produced, the Xe⁺ions are drawn to a negatively-biased sputter target which has beencoated with cesium vapor or other suitable alkaline material. Theenergetic Xe⁺ ions sputter away the neutral target atoms, some of whichpick up an electron while leaving the target surface due to the negativeelectron affinity of the cesium coating. Once negatively charged, thetarget ions are repelled from the target and can be collected from theion source by electrostatic ion optics and focused into a negative ionbeam. While it is possible to produce semiconductor dopant ions such asboron by this method, the ion currents tend to be low, the beamemittance tends to be large, and the presence of cesium vapor presents anearly unacceptable risk to wafer yield, since alkaline metals areconsidered very serious contaminants to silicon processing. Hence, amore commercially viable negative ion source technology is needed.

[0010] Of particular interest in semiconductor manufacturing process isthe formation of p-n junctions within the semiconductor substrate. Thisrequires the formation of adjacent regions of n-type and p-type doping.One general example of the formation of a junction is the implantationof n-type dopant into a semiconductor region already containing auniform distribution of p-type dopant. In such a case, an importantparameter is the junction depth, which is defined as the depth from thesemiconductor surface at which the n-type and p-type dopants have equalconcentrations. This junction depth is dependent primarily on theimplanted dopant mass, energy and dose.

[0011] An important aspect of modem semiconductor technology is thecontinuous evolution to smaller and faster devices. This process iscalled scaling. Scaling is driven by the continuous development ofimprovements to the lithographic process, allowing the definition ofsmaller and smaller features in the semiconductor substrate containingthe integrated circuit. A generally accepted scaling theory has beendeveloped to guide chip manufacturers in the appropriate resize of allaspects of the semiconductor device design at the same time, i.e., ateach technology or scaling node. The greatest impact of scaling on ionimplantation process is the scaling of junction depths, which requiresincreasingly shallow junctions as the device dimensions are decreased.The requirement for increasingly shallow junctions as integrated circuittechnology scales translates into the following requirement: ionimplantation energies must be reduced with each scaling step. Recently,the ion energy required for many critical implants has decreased to thepoint that conventional ion implantation systems, which were originallydeveloped to generate much higher energy beams, are not effective atproviding the necessary implant. These extremely shallow junctions aretermed “Ultra-Shallow Junctions” or USJ.

[0012] The limitations of conventional ion implantation systems at lowbeam energy are most evident in the extraction of ions from the ionsource, and their subsequent transport through the implanter's beamline. Ion extraction is governed by the Child-Langmuir relation whichstates that the extracted beam current density is proportional to theextraction voltage (i.e., beam energy at extraction) raised to the{fraction (3/2)} power. FIG. 1 is a graph of maximum extracted arsenicbeam current versus extraction voltage. For simplicity, an assumptionhas been made that only ⁷⁵As⁺ ions are present in the extracted beam.FIG. 1 shows that as the energy is reduced, extraction current dropsquickly. In a conventional ion implanter, this regime of“extraction-limited” operation is seen at energies less than about 10keV. Similar constraints occur in transporting the low-energy beam. Alower energy ion beam travels with lower velocity, and hence for a givenvalue of beam current the ions are closer together, i.e., the iondensity increases. This can be seen from the relation J=nev, where J isthe ion beam current density in mA/cm², n is the ion density in cm⁻³, eis the electronic charge (=6.02×10⁻¹⁹ Coulombs), and v is the averageion velocity in cm/s. Since the electrostatic force between ions isinversely proportional to the square of the distance between them, thismutually repulsive force is much stronger at low energy, and thusdisperses the ion beam. This phenomenon is called “beam blow-up”. Whilelow-energy electrons present in the implanter's beam line tend to betrapped by the positively-charged ion beam and help compensate forspace-charge blow-up during transport, nevertheless blow-up stilloccurs, and most pronounced in the presence of electrostatic focusinglenses, which tend to strip away the loosely-bound, highly mobilecompensating electrons from the beam. Low-energy beam transport can bedifficult for massive atoms such as arsenic (75 amu), since at a givenion energy, the ion velocity is lower than for lighter atoms. Severeextraction and transport difficulties also exist for the p-type dopant,boron. Boron transport is made difficult by the extremely lowimplantation energies (e.g., less than 1 keV) required by certainleading edge processes, and the fact that most of the ions extracted andtransported from a typical BF₃ source plasma are not the desired ion¹¹B⁺, but rather ion fragments, such as ¹⁹F⁺ and ⁴⁹BF₂ ⁺, which serve toincrease the charge density and average mass of the extracted ion beam.Looking to the future of VLSI semiconductor manufacturing, thesedifficulties in transporting significant currents of low-energy As and Bcombine to make the formation of USJ very challenging.

[0013] One way to benefit from the Child-Langmuir equation discussedabove is to increase the mass of the ion, for example, as illustrated inFIG. 1a, by ionizing a molecule containing the dopant of interest,rather than a dopant atom. In this way, while the kinetic energy of themolecule is higher during transport, upon entering the substrate, themolecule breaks up into its constituent atoms, sharing the energy of themolecule among the individual atoms according to their distribution inmass, so that the dopant atom's implantation energy is much lower thanits original transport kinetic energy. Consider a dopant atom “X” boundto a radical “Y” (disregarding for argument's sake the question ofwhether “Y” affects the device-forming process). If the ion XY⁺ wereimplanted in lieu of X⁺, then XY⁺ must be extracted and transported at ahigher energy, increased by a factor equal to the {(mass of XY)/(mass ofX)}; this ensures that the velocity of X remains unchanged. Since thespace-charge effects described by the Child-Langmuir equation discussedabove are superlinear with respect to ion energy, the maximumtransportable ion current is increased. Historically, the use ofpolyatomic molecules to address the problems of low energy implantationis known in the art. A common example has been the use of the BF₂ ⁺molecular ion for the implantation of low-energy boron, in lieu of B⁺.This process dissociates BF₃ feed gas to the BF₂ ⁺ ion for implantation.In this way, the ion mass is increased to 49 AMU, allowing an increaseof the extraction and transport energy by almost a factor of 5 (i.e.,{fraction (49/11)}) over using single boron atoms. Upon implantation,however, the boron energy is reduced by the same factor of ({fraction(49/11)}). We note that this approach does not reduce the currentdensity in the beam, since there is only one boron atom per unit chargein the beam. In addition, this process also implants fluorine atoms intothe semiconductor substrate along with the boron, however fluorine hasbeen known to exhibit adverse effects on the semiconductor device.

[0014] There has also been molecular ion work using decaborane as apolyatomic molecule, for ion implantation, as reported by Jacobson etal., “Decaborane, an alternative approach to ultra low energy ionimplantation”, IEEE Proceedings of the XIII^(tIh) InternationalConference on Ion Implantation Technology, Alpsbach, Austria, pp.300-303 (2000), and by Yamada, “Applications of gas cluster ion beamsfor materials processing”, Materials Science and Engineering A217/218,pp. 82-88 (1996). In this case, the implanted particle was an ion of thedecaborane molecule, B₁₀H₁₄, which contains 10 boron atoms, and istherefore a “cluster” of boron atoms. This technique not only increasesthe mass of the ion, but for a given ion current, it substantiallyincreases the implanted dose rate, since the decaborane ion B₁₀H_(x) ⁺has ten boron atoms per unit charge. This is a very promising technologyfor the formation of USJ p-type metal-oxide-semiconductor (PMOS)transistors in silicon, and in general for implanting very low-energyboron. Significantly reducing the electrical current carried in the ionbeam (by a factor of 10 in the case of decaborane ions), not onlyreduces beam space-charge effects, but wafer charging effects as well.Since charging of the wafer, particularly the gate oxides, by positiveion beam bombardment, is know to reduce device yields by damagingsensitive gate isolation, such a reduction in electrical current throughthe use of cluster ion beams is very attractive for USJ devicemanufacturing, which must increasingly accomodate exceedingly low gatethreshold voltages. It is to be noted that in these two examples ofP-type molecular implantation, the ions are created by simple ionizationof the feed material rather than by the conglomeration of feed materialinto clusters. It is also to be noted that there has not, until now,been a comparable technology developed for producing n-type moleculardopant ions. The future success of complementarymetal-oxide-semiconductor (CMOS) processing may well depend on thecommercialization of viable N- and P-type polyatomic implantationtechnologies. Thus there is a need to solve two distinct problems facingthe semiconductor manufacturing industry today: wafer charging, and lowproductivity in low-energy ion implantation.

[0015] Ion implanters have historically been segmented into threefundamental types: high current, medium current, and high energyimplanters. Cluster beams are useful for high current and medium-currentimplantation processes. More particularly, today's high currentimplanters are primarily used to form the low-energy, high dose regionsof the transistor such as drain structures and doping of the polysilicongates. They are typically batch implanters, i.e., processing many wafersmounted on a spinning disk, while the ion beam remains stationary. Highcurrent beam lines tend to be simple and incorporate a large acceptanceof the ion beam; at low energy and high currents, the beam at thesubstrate tends to be large, with a large angular divergence.Medium-current implanters typically incorporate a serial (one wafer at atime) process chamber, which offers a high tilt capability (e.g., up to60 degrees from substrate normal). The ion beam is typicallyelectromagnetically scanned across the wafer in an orthogonal direction,to ensure dose uniformity. In order to meet commercial implant doseuniformity and repeatability requirements of typically only a fewpercent variance, the ion beam should have excellent angular and spatialuniformity (angular uniformity of beam on wafer of <2 deg, for example).Because of these requirements, medium-current beam lines are engineeredto give superior beam control at the expense of limited acceptance. Thatis, the transmission efficiency of the ions through the implanter islimited by the emittance of the ion beam. Presently, the generation ofhigher current (about 1 mA) ion beams at low (<10 keV) energy isproblematic in serial implanters, such that wafer throughput isunacceptably low for certain lower-energy implants (for example, in thecreation of source and drain structures in leading-edge CMOS processes).Similar transport problems also exist for batch implanters (processingmany wafers mounted on a spinning disk) at the low beam energies of <5keV per ion.

[0016] While it is possible to design beam transport optics which arenearly aberration-free, the ion beam characteristics (spatial extent,spatial uniformity, angular divergence and angular uniformity) arenonetheless largely determined by the emittance properties of the ionsource itself (i.e., the beam properties at ion extraction whichdetermine the extent to which the implanter optics can focus and controlthe beam as emitted from the ion source). The use of cluster beamsinstead of monomer beams can significantly enhance the emittance of anion beam by raising the beam transport energy and reducing theelectrical current carried by the beam. Thus, there is a need forcluster ion and cluster ion source technology in semiconductormanufacturing to provide a better-focused, more collimated and moretightly controlled ion beam on target, in addition to providing highereffective dose rates and higher throughputs.

SUMMARY OF THE INVENTION

[0017] An object of this invention is to provide a method ofmanufacturing a semiconductor device, this method being capable offorming ultra-shallow impurity-doped regions of n-type (i.e., acceptor)conductivity in a semiconductor substrate, and furthermore to do so withhigh productivity.

[0018] Another object of this invention is to provide a method ofmanufacturing a semiconductor device, this method being capable offorming ultra-shallow impurity-doped regions of either N- or P-type(i.e., acceptor or donor) through the use of N- and P-type clusters ofthe form As_(n)H_(x) ⁺, where n=3 or 4 and 0≦x≦n+2 for the N-typecluster, and either B₁₀H_(x) ⁺ or B₁₀H_(x) ⁻ for the P-type cluster.

[0019] A further object of this invention is to provide a method ofimplanting arsenic cluster ions of the form As₃H_(x) ⁺ and As₄H_(x) ⁺,the method being capable of forming ultra-shallow implanted regions of nconductivity type in a semiconductor substrate.

[0020] A further object of this invention is to provide a method ofmaking phosphorus cluster ions of the form P_(n)H_(x) ⁺, where n equals2, 3, or 4 and x is in the range 0≦x≦6 by ionizing PH₃ feed gas, andsubsequently implanting said phosphorus cluster into a semiconductorsubstrate to accomplish N-type doping.

[0021] A further object of this invention is to provide a method ofmaking boron cluster ions of the form B_(n)H_(x) ⁺, where n equals 2, 3,or 4 and x is in the range 0≦x≦6 by ionizing B₂H₆ feed gas, andsubsequently implanting said boron cluster into a semiconductorsubstrate to accomplish P-type doping.

[0022] A still further object of this invention is to provide for an ionimplantation system for manufacturing semiconductor devices, which hasbeen designed to form ultra shallow impurity doped regions of either Nor P conductivity type in a semiconductor substrate through the use ofcluster ions.

[0023] According to one aspect of this invention, there is provided amethod of implanting cluster ions comprising the steps of: providing asupply of dopant atoms or molecules into an ionization chamber,combining the dopant atoms or molecules into clusters containing aplurality of dopant atoms and ionizing the dopant clusters into dopantcluster ions, extracting and accelerating the dopant cluster ions withan electric field, mass analyzing the ion beam, and implanting thedopant cluster ions into a semiconductor substrate.

[0024] An object of this invention is to provide a method that allowsthe semiconductor device manufacturer to ameliorate the difficulties inextracting low energy ion beams by implanting a cluster of n dopantatoms (n=4 in the case of As₄H_(x) ⁺) rather than implanting a singleatom at a time. The cluster ion implant approach provides the equivalentof a low energy, monatomic implant since each atom of the cluster isimplanted with an energy of E/n. Thus, the implanter is operated at anextraction voltage n times higher than the required implant energy,which enables higher ion beam current, particularly at the lowimplantation energies required by USJ formation. Considering the ionextraction stage, the relative improvement enabled by cluster ionimplant can be quantified by evaluating the Child-Langmuir limit. It isrecognized that this limit can be approximated by:

J _(max)=1.72(Q/A)^(1/2) V ^(3/2) d ⁻²,  (1)

[0025] where J_(max) is in mA/cm², Q is the ion charge state, A is theion mass in AMU, V is the extraction voltage in kV, and d is the gapwidth in cm. FIG. 1 is a graph of Eq. (1) for the case of ⁷⁵As⁺ withd=1.27 cm. In practice, the extraction optics used by many ionimplanters can be made to approach this limit. By extension of Eq. (1),the following figure of merit, Δ, can be defined to quantify theincrease in throughput, or implanted dose rate, for a cluster ionimplant relative to monatomic implantation:

Δ=n(U _(n) /U ₁)^(3/2)(m _(n) /m ₁)^(−1/2).  (2)

[0026] Here, Δ is the relative improvement in dose rate (atoms/sec)achieved by implanting a cluster with n atoms of the dopant of interestat an energy U_(n) relative to the single atom implant of an atom ofmass m₁ at energy U₁, where U₁=eV. In the case where U_(n) is adjustedto give the same dopant implantation depth as the monatomic (n=1) case,equation (2) reduces to:

ΔA=n².  (3)

[0027] Thus, the implantation of a cluster of n dopant atoms has thepotential to provide a dose rate n² higher than the conventional implantof single atoms. In the case of As₄H_(x), for small x, this maximum doserate improvement is about a factor of sixteen. A comparison betweenlow-energy As and As₄ implantation is shown in FIG. 2 to illustrate thispoint.

[0028] The use of clusters for ion implant also addresses the transportof low-energy ion beams. It is to be noted that the cluster ion implantprocess only requires one electrical charge per cluster, rather thanhaving every dopant atom carrying one electrical charge, as in theconventional case. The transport efficiency (beam transmission) is thusimproved, since the dispersive Coulomb forces are reduced with areduction in charge density. In addition, the clusters have higher massthan their monomers, and are therefore less affected by the intra-beamCoulomb forces. Thus, implanting with clusters of n dopant atoms ratherthan with single atoms ameliorates basic transport problems in lowenergy ion implantation and enables a dramatically more productiveprocess.

[0029] Enablement of this method requires the formation of said clusterions. The conventional sources used in commercial ion implanters produceonly a very small fraction of primarily lower-order (e.g., n=2) clustersrelative to their production of monomers, and hence these implanterscannot effectively realize the low-energy cluster beam implantationadvantages listed above. Indeed, the intense plasmas provided by manyconventional ion sources rather dissociate molecules and clusters intotheir component elements. The novel ion source described herein producescluster ions in abundance due to its use of a “soft” ionization process,namely electron-impact ionization by energetic primary electrons. Theion source of the present invention is designed expressly for thepurpose of producing and preserving dopant cluster ions.

DESCRIPTION OF THE DRAWING

[0030] These and other advantages of the present invention will bereadily understood with reference to the following specification andattached drawing wherein:

[0031]FIG. 1 is a graphical diagram illustrating maximum ⁷⁵As⁺ beamcurrent vs. extraction energy according to the Child-Langmuir Law.

[0032]FIG. 1a is a graphical diagram illustrating a comparison ofmaximum extraction current achievable through tetramer arsenic andmonomer arsenic.

[0033]FIG. 2 is a simplified diagram of the cluster ion source inaccordance with the present invention.

[0034]FIG. 2a is a perspective diagram of an exemplary embodiment of thecluster ion source in accordance with the present invention.

[0035]FIG. 3 is a simplified diagram of an exemplary cluster ionimplantation system in accordance with the present invention.

[0036]FIG. 4a is a diagram of a CMOS fabrication sequence duringformation of the NMOS drain extension.

[0037]FIG. 4b is a diagram of a CMOS fabrication sequence duringformation of the PMOS drain extension.

[0038]FIG. 5 is a diagram of a semiconductor substrate in the process ofmanufacturing an NMOS semiconductor device, at the step of n-type drainextension implant.

[0039]FIG. 5a is a diagram of a semiconductor substrate in the processof manufacturing a NMOS semiconductor device, at the step of thesource/drain implant.

[0040]FIG. 5b is a diagram of a semiconductor substrate in the processof manufacturing an PMOS semiconductor device, at the step of n-typedrain extension implant.

[0041]FIG. 5c is a diagram of a semiconductor substrate in the processof manufacturing a PMOS semiconductor device, at the step of thesource/drain implant.

[0042]FIG. 6 is a graphical diagram of a mass spectrum of PH₃ generatedwith the ion source of the present invention.

[0043]FIG. 7 is a graphical diagram of a mass spectrum of AsH₃ generatedwith the ion source of the present invention.

[0044]FIG. 8 is a graphical illustration demonstrating On-wafer As₄H_(x)⁺ ion currents in the low energy range.

[0045]FIG. 9 is a graphical illustration of the data illustrated in FIG.6 converted to units of beam brightness.

[0046]FIG. 10 is a graphical illustration of as-implanted SIMS profilesof arsenic concentrations from AsH_(x) ⁺ and As₄H_(x) ⁺ ion beamsimplanted into silicon wafers using the present invention, andcomparison with TRIM calculations.

[0047]FIG. 11 is a graphical illustration of a mass spectrum of B₂H₆generated with the ion source of the present invention.

[0048]FIG. 12 is a graphical illustration of recorded positive-ion massspectrum for the present invention operating with decaborane feedmaterial.

[0049]FIG. 13 is a graphical illustration of recorded negative-ion massspectrum for the present invention operating with decaborane feedmaterial.

[0050]FIG. 14 is a graphical illustration of recorded mass spectrum ofboth negative-ion and positive-ion decaborane taken in succession, alsoshowing the dimer, B₂₀H_(x). FIG. 15 is a graphical illustration ofas-implanted SIMS profiles of negative and positive B₁₀H_(x) ions usingthe present invention, at a decaborane implantation energy of 20 keV.

[0051]FIG. 16 is a graphical illustration of as-implanted SIMS profilesof 20 keV decaborane implanted into silicon, showing B concentration andH concentration.

DETAILED DESCRIPTION

[0052]FIG. 2 is a conceptual diagram of a cluster ion source 10 and itsvarious components. A supply of feed gas 11 is provided, such as acylinder of AsH₃, PH₃, B₂H₆ or vaporized B₁₀H₁₄. The feed material canbe stored in a cylinder as a gas at room temperature, or can beintroduced as vapor sublimated from a heated solid or evaporated from aliquid phase. The feed gas supply 11 is connected to an ionizationchamber 13 through a flow controller 12. The flow controller 12 can beas sophisticated as a computer-controlled mass flow controller, or assimple as a connecting tube with predetermined gas conductance. In thelatter case, the flow is varied by controlling the pressure of the gasin 11. The controlled flow of dopant-containing gaseous feed materialcreates a stable gas pressure within the ionization chamber 13, forexample, between approximately 3×10⁻⁴ Torr and 3×10⁻³ Torr. Ionizationenergy 14 is provided in the form of a controlled current of electronswith a defined energy or velocity. The temperature of ionization chamber13 and indeed of all the components of the ion source is typicallycontrolled to a desired value. By tuning the source pressure,temperature, electron current, and electron energy, an environment iscreated within the ionization chamber 13 such that the dopant atoms ormolecules of, for example, AsH₃, combine to form cluster ions thatcontain more than one atom of the desired dopant element, for example,the tetramer compound As₄H_(x) ⁺, where x is an integer between 0 and 4.

[0053] An aperture 17 in the ionization chamber 13 allows ions to escapeinto the beam path, extracted by a strong electric field betweenionization chamber 13 and an extraction electrode 15. This extraction,or accelerating, field is generated by a high voltage power supply whichbiases the ionization chamber 13 to a voltage V relative to groundpotential, the extraction electrode 15 being near ground potential. Theaccelerating field is established in the forward direction to attractpositive ions out of the ionization chamber 13, and in the reversedirection when negative ions are desired. The accelerated ions areformed into an ion beam 16 by the extraction electrode 15. The kineticenergy E of ion beam 16 is given by Equation (4):

E=/qV/,  (4)

[0054] where V is the source potential, and q is the electric charge perion. When V is expressed in volts and q is expressed in units ofelectronic charge, E has units of electron-volts (eV).

[0055] The ion source described herein is one embodiment of a novelelectron impact ionization source. FIG. 2a is a cross-sectionalschematic diagram of the source construction which serves to clarify thefunctionality of the components which make up the ion source 10. The ionsource 10 is made to interface to an evacuated vacuum chamber of an ionimplanter or other process tool by way of a mounting flange 36. Thus,the portion of the ion source 10 to the right of flange 36, shown inFIG. 2a, is at high vacuum (pressure <1×10⁻⁴ Torr). Gaseous material isintroduced into the ionization chamber 44 in which the gas molecules areionized by electron impact from opposed electron beams 70 a and 70 b,which enter the ionization chamber 44 through entrance apertures 71 aand 71 b, respectively, such that electron beams 70 a and 70 b arealigned with ion extraction aperture 81. Thus, ions are created adjacentto the ion extraction aperture 81, which appears as a slot in the ionextraction aperture plate 80. The ions are then extracted and formedinto an energetic ion beam by an extraction electrode (not shown)located in front of the ion extraction aperture plate 80.

[0056] Gases may be fed into the ionization chamber 44 via a gas conduit33. Solid feed materials can be vaporized in a vaporizer 28, and thevapor fed into the ionization chamber 44 through a vapor conduit 32.Solid feed material 29, located under a perforated separation barrier 34a, is held at a uniform temperature by temperature control of thevaporizer housing 30. Vapor 50 which accumulates in a ballast volume 31feeds through conduit 39 and through one or more shutoff valves 100 and110. The vapor 50 then feeds into the ionization chamber 44 through avapor conduit 32, located in the source block 35. Thus, both gaseous andsolid dopant-bearing materials may be ionized by this ion source.

[0057] The method herein described can be considered normal operation ofthe ion source of the present invention where the only difference fromother operational modes is the user's choice of values for the sourceparameters (feed material, feed gas flow rate, electron ionizationenergy and current, and source component temperature(s)). In the caseillustrated in FIG. 2a, where AsH₃ is the feed gas, typical values ofthese source parameters were: AsH₃ flow rate=2.5 sccm, electronionization energy=1.7 keV, electron current=100 mA, and ionizationchamber temperature=200 C. One aspect of the ion source of the presentinvention is user control of the ionization chamber temperature, as wellas the temperature of the source block and valves. The source utilizes acombination of heating and cooling to achieve accurate control of thesource temperature. Separate temperature control is provided forvaporizer 28, shutoff valves 100 and 110, source block 35, andionization chamber 44. External electronic controllers (such as an Omronmodel E5CK) are used for temperature control. Heating is provided byembedded resistive heaters, whose heating current is controlled by theelectronic controller. Cooling is provided by a combination ofconvective and conductive gas cooling methods, as further described, forexample, in commonly owned PCT application US01/18822, and in U.S.application Ser. No. 10/183,768, both herein incorporated by reference.

[0058]FIG. 3 shows the ion source in conjunction with key downstreamelements which comprise a proposed cluster ion implantation system.Configurations other than that shown in FIG. 3 are possible. The ionsource 21 is coupled with extraction electrode 22 to create an ion beam20 which contains cluster ions. The ion beam 20 typically contains ionsof many different masses, i.e., all of the species for which ions of agiven charge polarity are created in the ion source 21. The ion beam 20then enters the analyzer magnet 23. The analyzer magnet 23 creates adipole magnetic field within the ion beam transport path depending onthe current in the magnet coils; the direction of the magnetic field isnormal to the plane of FIG. 3. The function of the analyzer magnet 23 isto spatially separate the ion beam into a set of constituent beamlets bybending the ion beam in an arc whose radius depends on themass-to-charge ratio of the discrete ions. Such an arc is shown in FIG.3 as a beam component 24, the selected ion beam. The magnet 23 bends agiven beam along a radius given by Equation (5) below:

R=(2mU)^(1/2) /qB  (5)

[0059] where R is the bending radius, B is the magnetic flux density, mis the ion mass, U is the ion kinetic energy and q is the ion chargestate.

[0060] The selected ion beam is comprised of ions of a narrow range ofmass-energy product only, such that the bending radius of the ion beamby the magnet sends that beam through a mass-resolving aperture 27. Thecomponents of the beam that are not selected do not pass through themass-resolving aperture 27, but are intercepted elsewhere. For beamswith smaller mass-to-charge ratios m/q than the selected beam 25, forexample comprised of hydrogen ions having masses of 1 or 2 atomic massunits, the magnetic field induces a smaller bending and the beamintercepts the inner radius wall 30 of the magnet chamber, or elsewhere.For beams with larger mass-to-charge ratios than the selected beam 26,the magnetic field induces a larger bending radius, and the beam strikesthe outer radius wall 29 of the magnet chamber, or elsewhere. As is wellestablished in the art, the combination of analyzer magnet 23 andmass-resolving aperture 27 comprise a mass analysis system which selectsthe ion beam 24 from the multi-species beam 20 extracted from the ionsource. The selected beam 24 can then pass through a post-analysisacceleration/deceleration stage 31. This stage 31 can adjust the beamenergy to the desired final energy value required for the specificimplantation process. The post-analysis acceleration/deceleration stage31 can take the form of an electrostatic lens, or alternatively a LINAC(linear accelerator), for example. In order to prevent ions which haveundergone charge-exchange or neutralization reactions between theresolving aperture and the wafer (and therefore do not possess thecorrect energy) from propagating to the wafer, a “neutral beam filter”or “energy filter” can be incorporated within this beam path. Forexample, the post-analysis acceleration/deceleration stage 31 canincorporate a “dogleg” or small-angle deflection in the beam path whichthe selected ion beam 24 is constrained to follow through an applied DCelectromagnetic field; beam components which have become neutral ormultiply-charged, however, would necessarily not follow this path. Theenergy-adjusted beam then enters a beam scanning system 32, in theimplantation system depicted in FIG. 3. The beam scanning system 32scans the beam so that the entire target 28 is uniformly implanted.Various configurations are possible, with one-dimensional ortwo-dimensional scanning, and electrostatic versus magnetic scanningsystems, for example.

[0061] The beam then enters the wafer process chamber 33, also held in ahigh vacuum environment, where it strikes the target 28. Variousconfigurations of wafer processing chambers, and wafer handling systemsare possible, the major categories being serial (one wafer at a time) orbatch (many wafers processed together on a spinning disk). In a serialprocess chamber, typically one dimension (either lateral or vertical) ismechanically scanned across the beam, which is electromagneticallyscanned in the orthogonal direction, to ensure good spatial uniformityof the implant. In a batch system, spinning of the disk providesmechanical scanning in the radial direction, and either vertical orhorizontal scanning of the spinning disk is also effected at the sametime, the ion beam remaining stationary.

[0062] For cluster ion implantation to provide accurate dopantplacement, it is necessary that each of n dopant atoms contained withinthe cluster penetrate the substrate with the same kinetic energy; in thesimplest case in which the molecular ion is of the form A_(n) ⁺ (thatis, it is uniquely comprised of n dopant atoms A), each of the n dopantatoms must receive the same fraction 1/n of the cluster's energy uponpenetration into the semiconductor substrate. It has been established,for example by Sze, in VLSI Technology, McGraw Hill, pp. 253-254 (1983),that this equal division of energy occurs whenever a polyatomic moleculeimpacts a solid target surface. Furthermore, it is necessary that theelectrical results of such implantation are the same as the equivalentimplant using single atom ion implantation. Such results have been shownby Jacobson et al., “Decaborane, an alternative approach to ultra lowenergy ion implantation”, IEEE Proceedings of the XIII^(tIh)International Conference on Ion Implantation Technology, Alpsbach,Austria, pp. 300-303 (2000), in detail for the case of implantation withdecaborane, and indeed we expect similar results for any dopant cluster.

[0063] During ion implantation, dopant atoms may penetrate more deeplyinto the semiconductor substrate by channeling, i.e., by entering thesubstrate crystal lattice along a symmetry direction which contains alow density of lattice atoms, or a “channel”. If the ion trajectorycoincides with the direction of a channel in the semiconductor crystallattice, the ion substantially avoids collisions with the substrateatoms, extending the range of the dopant projectile. An effective meansto limit or even prevent channeling consists of forming an amorphouslayer at the surface of the substrate. One means of creating such alayer is to implant the substrate either with ions of the sameelement(s) of which the substrate consists or with ions having the sameelectrical properties (i.e., from the same column of the periodictable), such that the crystal damage caused by the implantation processis sufficient to eliminate the crystalline structure of a layer at thesubstrate surface without subsequently altering the electricalproperties of the substrate during the activation step. For example,silicon or germanium ions may be implanted into a silicon substrate atan energy of 20 keV at a dose of 5×10¹⁴ cm⁻² to form such an amorphouslayer in a silicon substrate, followed by the implantation of theshallow dopant layer by cluster ion implantation.

[0064] An important application of this method is the use of cluster ionimplantation for the formation of n- and p-type shallow junctions aspart of a CMOS fabrication sequence. CMOS is the dominant digitalintegrated circuit technology in current use and its name denotes theformation of both n-channel and p-channel MOS transistors (ComplementaryMOS: both n and p) on the same chip. The success of CMOS is that circuitdesigners can make use of the complementary nature of the oppositetransistors to create a better circuit, specifically one that draws lessactive power than alternative technologies. It is noted that the n and pterminology is based on negative and positive (n-type semiconductor hasnegative majority carriers, and vice versa), and the n-channel andp-channel transistors are duplicates of each other with the type(polarity) of each region reversed. The fabrication of both types oftransistors on the same substrate requires sequentially implanting ann-type impurity and then a p-type impurity, while protecting the othertype of devices with a shielding layer of photoresist. It is noted thateach transistor type requires regions of both polarities to operatecorrectly, but the implants which form the shallow junctions are of thesame type as the transistor: n-type shallow implants into n-channeltransistors and p-type shallow implants into p-channel transistors. Anexample of this process is shown in FIGS. 4a and 4 b. In particular,FIG. 4a illustrates a method for forming the n-channel drain extension89 through an n-type cluster implant 88, while FIG. 4b shows theformation of the p-channel drain extension 90 by a p-type clusterimplant 91. It is to be noted that both N- and P-types of transistorsrequires shallow junctions of similar geometries, and thus having bothn-type and p-type cluster implants is advantageous for the formation ofadvanced CMOS structures.

[0065] An example of the application of this method is shown in FIG. 5for the case of forming an NMOS transistor. This figure showssemiconductor substrate 41 which has undergone some of the front-endprocess steps of manufacturing a semiconductor device. The structureconsists of a N-type semiconductor substrate 41 that has been processedthrough the p-well 43, trench isolation 42, and gate stack formation 44,45 steps. The p-well 43 forms a junction with the n-type substrate 41that provides junction isolation for the transistors in the well. Thetrench isolation 42 provides lateral dielectric isolation between the N-and P-wells (i.e., in the overall CMOS structure). The gate stack isthen constructed, containing the gate oxide layer 44 and the polysilicongate electrode 45, which have been patterned to form the transistor gatestack. Also, photoresist 46 has been applied and patterned such that thearea for NMOS transistors is open, but other areas of the substrate areshielded by the photoresist layer 46. At this point in the process flow,the substrate is ready for the drain extension implant, which is theshallowest doping layer required by the device fabrication process. Atypical process requirement for leading-edge devices of the 0.13 μmtechnology node is an arsenic implant energy of between 1 keV and 2 keV,and an arsenic dose of 5×10¹⁴ cm⁻². The cluster ion beam 47, As₄H_(x) ⁺in this case, is directed at the semiconductor substrate, typically suchthat the direction of propagation of the ion beam is normal to thesubstrate, to avoid shadowing by the gate stack. The energy of theAs₄H_(x) ⁺ cluster should be four times the desired As⁺ implant energy,e.g., between 4 keV and 8 keV. The clusters dissociate upon impact withthe substrate, and the dopant atoms come to rest in a shallow layer nearthe surface of the semiconductor substrate, which forms the drainextension region 48. We note that the same implant enters the surfacelayer of the gate electrode 49, providing additional doping for the gateelectrode. The process described in FIG. 5 is thus one importantapplication of the proposed invention.

[0066] A further example of the application of this method is shown inFIG. 5a: the formation of the deep source/drain regions. This figureshows the semiconductor substrate 41 of FIG. 5 after execution offurther processes steps in the fabrication of a semiconductor device.The additional process steps include the formation of a pad oxide 51 andthe formation of spacers 52 on the sidewalls of the gate stack. At thispoint, a photoresist layer 53 is applied and patterned to expose thetransistor to be implanted, an NMOS transistor in this example. Next,the ion implant to form the source and drain regions 55 is performed.Since this implant requires a high dose at low energy, it is anappropriate application of the proposed cluster implantation method.Typical implant parameters for the 0.13 μm technology node areapproximately 6 keV per arsenic atom (54) at an arsenic dose of 5×10¹⁵cm⁻², so it requires a 24 keV, 1.25×10¹⁵ cm⁻² As₄H_(x) ⁺ implant, a 12keV, 2.5×10¹⁵ cm⁻² As₂H_(x) ⁺ implant, or a 6 keV, 5×10¹⁵ cm⁻² As⁺implant. As shown in FIG. 5, the source and drain regions 55 are formedby this implant. These regions provide a high conductivity connectionbetween the circuit interconnects (to be formed later in the process)and the intrinsic transistor defined by the drain extension 48 inconjunction with the channel region 56 and the gate stack 44, 45. It maybe noted that the gate electrode 45 can be exposed to this implant (asshown), and if so, the source/drain implant provides the primary dopingsource for the gate electrode. This is shown in FIG. 5a as the polydoping layer 57.

[0067] The detailed diagrams showing the formation of the PMOS drainextension 148 and PMOS source and drain regions 155 are shown in FIGS.5b and 5 c, respectively. The structures and processes are the same asin FIGS. 5a and 5 b with the dopant types reversed. In FIG. 5b, the PMOSdrain extension 148 is formed by the implantation of a boron clusterimplant 147. Typical parameters for this implant would be an implantenergy of 500 eV per boron atom with a dose of 5×10¹⁴ cm⁻², for the 0.13um technology node. Thus, a B₁₀H_(x) implant would be at 5 keV and adecaborane dose of 5×10¹³ cm⁻². FIG. 5c shows the formation of the PMOSsource and drain regions 148, again by the implantation of a p-typecluster ion beam 154 such as decaborane. Typical parameters for thisimplant would be an energy of around 2 keV per boron atom with a borondose of 5×10¹⁵ cm⁻² (i.e., 20 keV decaborane at 5×10¹⁴ cm⁻²) for the0.13 um technology node.

[0068] In general, ion implantation alone is not sufficient for theformation of an effective semiconductor junction: a heat treatment isnecessary to electrically activate the implanted dopants. Afterimplantation, the semiconductor substrate's crystal structure is heavilydamaged (substrate atoms are moved out of crystal lattice positions),and the implanted dopants are only weakly bound to the substrate atoms,so that the implanted layer has poor electrical properties. A heattreatment, or anneal, at high temperature (greater than 900C) istypically performed to repair the semiconductor crystal structure, andto position the dopant atoms substitutionally, i.e., in the position ofone of the substrate atoms in the crystal structure. This substitutionallows the dopant to bond with the substrate atoms and becomeelectrically active; that is, to change the conductivity of thesemiconductor layer. This heat treatment works against the formation ofshallow junctions, however, because diffusion of the implanted dopantoccurs during the heat treatment. Boron diffusion during heat treatment,in fact, is the limiting factor in achieving USJ's in the sub-0.1 micronregime. Advanced processes have been developed for this heat treatmentto minimize the diffusion of the shallow implanted dopants, such as the“spike anneal”. The spike anneal is a rapid thermal process wherein theresidence time at the highest temperature approaches zero: thetemperature ramps up and down as fast as possible. In this way, the hightemperatures necessary to activate the implanted dopant are reachedwhile the diffusion of the implanted dopants is minimized. It isanticipated that such advanced heat treatments would be utilized inconjunction with the present invention to maximize its benefits in thefabrication of the completed semiconductor device.

[0069]FIG. 6 demonstrates the creation of phosphorus cluster ions andthe formation of mass-resolved phosphorus cluster ion beams. This massspectrum shows data taken during of operation of the ion source of thepresent invention, using phosphine (PH₃) as the source feed gas. Thismass spectrum shows the intensity of ion current on the vertical scale61 versus analyzer magnetic field, which determines ion mass-to-chargeratio, on horizontal scale 62. Currents were measured in a Faraday cupin which secondary electrons were effectively suppressed. Horizontalscale 62, being linear with magnetic field, is nonlinear inmass-to-charge ratio, since for a given extraction voltage V the twoquantities are related by m/q=aB², where a is a constant. This makeshigher mass peaks closer together on horizontal scale 62. The phosphorusclusters are observed as the signals 65, 66 and 67 having two, three andfour phosphorus atoms per cluster, respectively. Analysis of thisspectrum demonstrates that the ion source of the present inventionsupports the formation and preservation of clusters during operation.The first grouping of signals 63, on the left of the graph, are thehydrogen ions, with mass numbers 1 and 2. The hydrogen peaks arerelatively small, much smaller than the phosphorus-containing peaks. Thesecond grouping of signals 64 occurs between masses 31 and 35 andcorrespond to ions containing one phosphorus atom. During a conventionalimplantation process, one, several, or all of these peaks might beimplanted, depending upon the choice of mass-resolving aperture 27 (seeFIG. 2) selected. Some applications might require selection of only the³¹P⁺ peak, if there is sensitivity to H in the process. In this case, anarrow mass-resolving aperture can be implemented to exclude the hydridepeaks, i.e., PH_(x) ⁺, where x=1,2,3, or 4. Other processes may requirethe implantation of all of the peaks within this group to increaseproductivity. The next group of signals to the right 65 consist of thephosphorus dimer P₂; each of these particles contains two phosphorusatoms. The leftmost significant signal corresponds to P₂ ⁺ with massnumber 62. The neighboring signals to the right are those for P₂H_(x) ⁺,where x is between one and six. We also note that the intensity of thesesignals is reduced in comparison to the monomer peaks 64, but theobserved intensity depends upon the entire set of source input settingsand can be optimized for a desired beam condition, for example tomaximize the relative height of the P₂ ⁺ peak if dimers are desired. Theselection of mass-resolving aperture determines how many of these beamswould be implanted during an implantation process. The next signalgrouping to the right 66 corresponds to the phosphorus cluster ionscontaining three phosphorus atoms (P₃ ⁺). The next signal to the right67 corresponds to the phosphorus cluster ions containing four phosphorusatoms. It is interesting to note that the intensity of this cluster ishigher than for the P₃H_(x) ⁺ cluster, and that the net dose rate usingthe P₄ ⁺ cluster (4× the observed intensity) exceeds that for implantingeither P⁺ or P₂ ⁺, and that the energy per phosphorus atom implanted isonly ¼ of the nominal ion beam energy.

[0070]FIG. 7 shows a mass spectrum of AsH₃ using the present invention.The ion beam energy was 19 keV, so that the effective As implant energyof As₄H_(x) ⁺ would be 4.75 keV. The beam current of As₄H_(x) ⁺ in FIG.7 was about 0.25 mA, so that the equivalent As dopant current is about 1mA. FIG. 7 also illustrates that particle currents between 0.5 mA and1.0 mA would result from implantation of As, As₂, As₃, or As₄-containingion beams, also giving an effective implant energy range of betweenabout 20 and 5 keV, by simply adjusting the analyzer magnet current toselect different parts of the spectrum of FIG. 7.

[0071]FIG. 8 shows As₄H_(x) ⁺ current as a function of As implantenergy. The angular divergence of the ion beam was limited by aperturesbetween the mass resolving aperture (e.g., see 27 of FIG. 3) and Faradaycup to a half-angle in the lateral or dispersive direction of 11 mR, orabout 0.6 deg. 1 keV/atom is a lower limit of what semiconductor processwill require for arsenic implantation into USJ devices.

[0072]FIG. 9 illustrates the beam currents of FIG. 8 converted to unitsof beam brightness, and comparison to a “typical” modem-daymedium-current implanter. The improvement is about a factor of 30 (themedium-current implanter specifications we assumed were: 40 mradhalf-angular acceptance, and 200 uA of beam current at 10 keV).Stephens, in Handbook of Ion Implantation Technology, J. F. Ziegler,ed., North-Holland, pp. 455-499 (1992), define brightness B at as:

B=2I/n ²ε² (μA-mm⁻²⁻ mrad ⁻²),  (6)

[0073] where I is the effective dopant beam current in microamperes, andε is the beam emittance in square (milliradians−millimeters). Emittanceis calculated by

ε=δα,  (7)

[0074] where δ is the beam half-width in the dispersive plane, and α isthe half-pencil angle, both measured at the image plane, i.e., at theresolving aperture location.

[0075] Beam brightness is an important figure of merit which quantifieshow much beam current can be transmitted into a certain acceptance, forexample through a tube of a certain diameter and length. Since ionimplanter beam lines have well-defined acceptances, brightness is animportant measure of productivity for emittance-limited beams. Emittanceis usually the limiting factor in the transport of low-energy beams. Wenote that this is largely the benefit of using cluster ions versusmonomer ions, as expressed in Equation (1)-(3). For As₄ implantation,Eq. (3) predicts a throughput increase of sixteen, i.e., Δ=n².

[0076]FIG. 10 shows Secondary Ion Mass Spectroscopy (SIMS) results forsilicon samples implanted with AsH_(x) ⁺ and As₄H_(x) ⁺ ions at 4.75 keVand 19 keV, respectively. Atomic doses were approximately 1×10¹⁶ cm⁻².These data are compared with a full dynamical scattering model, TRIM,which is commonly used in the industry to simulate ion implantation intosilicon. The results indicate that we are indeed implanting As and As₄at the designated energies.

[0077]FIG. 11 shows a mass spectrum of diborane, B₂H₆, a gaseousmaterial not commonly used in conventional ion implantation, butcommercially available. FIG. 11 shows groupings of H (H⁺, H₂ ⁺, H₃ ⁺), B(B, BH⁺, BH₂ ⁺), B₂ (B₂ ⁺, B₂H⁺, B₂H₂ ⁺, B₂H₃ ⁺, B₂H₄ ⁺), B₃ (B₃, B₃H⁺,B₃H₂ ⁺, B₃H₃ ⁺, B₃H₄ ⁺), B₄ (B4, B₄H⁺, B₄H₂ ⁺, B₄H₃ ⁺, B₄H₄ ⁺), and a B₅group. The spectrum of FIG. 11 is somewhat complicated in it'sinterpretation because there are two naturally-occuring isotopes ofboron present, ¹⁰B and ¹¹B, which are represented in about a 4:1 ratioof ¹¹B to ¹⁰B, reflecting their natural abundances. For example, both¹¹B and ¹⁰BH are present in the peak at 11 amu.

[0078]FIG. 12 demonstrates the creation of boron hydride clusters andpositive cluster ions in the present invention. This mass spectrum showsdata taken during of operation of the ion source of the presentinvention, using vaporized decaborane B₁₀H₁₄ as the source feedmaterial. Boron hydride clusters of the form B_(y)H_(x) ⁺ with 1≦y≦10and 0≦x≦14 are shown, separated by 1 amu from 1 amu to about 124 amu.The largest signal observed, B₁₀H_(x) ⁺, corresponds to decaboranemolecular ions, which are formed by direct ionization of the decaboraneparent molecule.

[0079]FIG. 13 shows a negative ion spectrum of decaborane produced bythe ion source of the present invention, analogous to the spectrum ofFIG. 12. Far fewer ion states are formed by negative decaborane ions, sothe majority (about 90%) of the ions are contained within the parentB₁₀H_(x) ⁻ peak. The use of negative ions for ion implantation ofsemiconductors is very beneficial since it virtually eliminates thewafer charging observed with positive ion implantation. It is unusualfor an ion source to produce abundant quantities of both positive andnegative ions of a given material; the peak ion currents of FIGS. 12 and13 are the same within a factor of two. This is shown dramatically inFIG. 14 for an extended mass range. These data were collected as shownby collecting a positive-ion mass spectrum, reversing the polarities ofthe ion implanter power supplies, and collecting a negative ion spectrumover the same mass range, on the same sheet of paper, with the ionimplantation system of the present invention. The Faraday cup currentswere fed to an x-y paper recorder in order to collect FIG. 14.Significant advantages are evident in implanting negative ions ratherthan positive ions in the case of decaborane: 1) more useful ion currentis within the peak of interest, resulting in greater useful dopant flux;2) the parent peak is narrower in mass by almost a factor of two (a fullwidth at half-maximum of five amu for the negative ions versus nine amufor the positive ions), and 3) the elimination of wafer charging, as isgenerally accepted in the art, when negative ions are substituted forpositive ions.

[0080]FIG. 15 shows SIMS profiles for both positive and negativedecaborane ions implanted into silicon samples at a decaborane energy of20 keV. The profiles are nearly identical, as one would expect if eachion possessed the same number of boron atoms, and thus are implanted tothe same projected range.

[0081]FIG. 16 shows SIMS data for a negative decaborane implant, showingalso H concentration. The H dose was 0.9 times the boron dose, whichsuggests an average chemical formula for negative decaborane of B₁₀H₉ ⁻.

[0082] There are several elements of interest for use in the formationof shallow junctions in semiconductors. For silicon applications, theprimary dopants are boron, phosphorus, arsenic and antimony, so theseelements have the largest potential application to the formation ofshallow junctions. Further, silicon and germanium implants are used toform amorphous regions in silicon, so clusters of these elements wouldbe useful for the formation of shallow amorphous regions. For compoundsemiconductors, elements of interest for shallow junctions includesilicon, germanium, tin, zinc, cadmium and beryllium, so clusters ofthese elements have opportunity in the formation of shallow junctions incompound semiconductor manufacturing.

[0083] One aspect of this method is providing the proper environmentwithin the ionization chamber for the formation of cluster ions. Each ofthe various elements discussed has different chemical properties and sothe optimal environment is different for each element. Each element andeach selected cluster will require a different set of the inputparameters to achieve optimal performance. The parameters available foroptimization include: the source pressure as controlled by the flow offeed material, the temperature inside the ionization chamber ascontrolled by the temperature control system, the ionization energyintensity and characteristics, such as the electron beam current andelectron energy when the ionization energy is an electron beam. Thesebasic parameters work together to create the appropriate environmentwithin the source ionization chamber for the formation and ionization ofthe dopant clusters.

[0084] As has been described above, the ion implantation of clusters ofdopant atoms makes it possible to implant both n-type and p-type dopantsat a shallow depth with high efficiency, as compared to the ionimplantation of single dopant atoms.

[0085] The present invention has been described, along with severalembodiments. The present invention is not limited thereto. For example,it will be apparent to those skilled in the art that variousmodifications, alterations, improvements and combination thereof arepossible. Obviously, many modifications and variations of the presentinvention are possible in light of the above teachings. Thus, it is tobe understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedabove.

What is claimed and desired to be covered by a Letters Patent is asfollows:
 1. A method of implanting dopant materials into a semiconductorsubstrate comprising: generating N-type dopant cluster ions As₄+; andimplanting said N-type As₄+ dopant cluster ions into a first region ofsaid substrate resulting in N-type doping of said substrate.
 2. Themethod as recited in claim 1, wherein said generating step comprises:providing a source of arsine (AsH₃) gas; providing a conduit betweensaid source of arsine (AsH₃) gas and an ionization chamber to enablesaid gaseous arsine (AsH₃) to communicate with said ionization chamber;and ionizing said arsine (AsH₃) gas in said ionization chamber.
 3. Themethod as recited in claim 2, wherein said ionizing step comprisesirradiation within said ionization chamber by one or more electronbeams.
 4. The method as recited in claim 2, further including the stepof controlling the temperature of said ionization chamber to apredetermined value.
 5. The method as recited in claim 2, wherein saidimplanting step includes the step of extracting As₄+ ions from saidionization chamber by an electric field.
 6. The method as cited in claim5, further including the step of mass analyzing the extracted ions byselecting the As₄+ ions.
 7. The method as recited in claim 1, furtherincluding the step of: generating P-type dopant cluster ions; andimplanting said P-type dopant cluster ions into said substrate into asecond region different than said first region.
 8. The method as recitedin claim 7, wherein said generating step comprises generating negativedecaborane cluster ions (B₁₀H_(x) ⁻), where x is an integer and 0≦x≦14.9. A method of implanting dopant materials into a semiconductorsubstrate comprising: generating N-type dopant cluster ions As₃ ⁺; andimplanting said N-type As₃ ⁺ dopant cluster ions into a first region ofsaid substrate resulting in N-type doping of said substrate.
 10. Themethod as recited in claim 9, wherein said generating step comprises:providing a source of arsine (AsH₃) gas; providing a conduit betweensaid source of arsine (AsH₃) gas and an ionization chamber to enablesaid gaseous arsine (AsH₃) to communicate with said ionization chamber;and ionizing said arsine (AsH₃) gas in said ionization chamber.
 11. Themethod as recited in claim 10, wherein said ionizing step comprisesirradiation within said ionization chamber by one or more electronbeams.
 12. The method as recited in claim 10, further including the stepof controlling the temperature of said ionization chamber to apredetermined value.
 13. The method as recited in claim 10, wherein saidimplanting step includes the step of extracting As₃ ⁺ ions from saidionization chamber by an electric field.
 14. The method as cited inclaim 13, further including the step of mass analyzing the extractedions by selecting the As₃ ⁺ ions.
 15. The method as recited in claim 9,further including the step of: generating P-type dopant cluster ions;and implanting said P-type dopant cluster ions into said substrate intoa second region different than said first region.
 16. The method asrecited in claim 15, wherein said generating step comprises generatingnegative decaborane cluster ions (B₁₀H_(x) ⁻), where x is an integer and0≦x≦14.
 17. A method of implanting dopant materials into a semiconductorsubstrate comprising: generating N-type dopant cluster ions As⁴H_(x) ⁺,where x is an integer and 1≦x≦6; implanting said N-type dopant clusterions into a first region of said substrate resulting in N-type doping ofsaid substrate.
 18. The method as recited in claim 17, wherein saidgenerating step comprises: providing a source of arsine (AsH₃) gas;providing a conduit between said source of arsine (AsH₃) gas and anionization chamber to enable said gaseous arsine (AsH₃) to communicatewith said ionization chamber; and ionizing said arsine (AsH₃) gas insaid ionization chamber.
 19. The method as recited in claim 18, whereinsaid ionizing step comprises irradiation within said ionization chamberby one or more electron beams.
 20. The method as recited in claim 18,further including the step of controlling the temperature of saidionization chamber to a predetermined value.
 21. The method as recitedin claim 18, wherein said implanting step includes the step ofextracting said dopant cluster ions from said ionization chamber by anelectric field.
 22. The method as cited in claim 21, further includingthe step of mass analyzing the extracted ions by selecting said dopantcluster ions.
 23. The method as recited in claim 17, further includingthe step of: generating P-type dopant cluster ions; and implanting saidP-type dopant cluster ions into said substrate into a second regiondifferent than said first region.
 24. The method as recited in claim 23,wherein said generating step comprises generating negative decaboranecluster ions (B₁₀H_(x) ⁻), where x is an integer and 0≦x≦14.
 25. Amethod of implanting dopant materials into a semiconductor substratecomprising: generating N-type dopant cluster ions As₃ Hx+, where x is aninteger and 1≦x≦5; and implanting said N-type As₃ Hx+, cluster ions intoa first region of said substrate resulting in N-type doping of saidsubstrate.
 26. The method as recited in claim 25, wherein saidgenerating step comprises: providing a source of arsine (AsH₃) gas;providing a conduit between said source of arsine (AsH₃) gas and anionization chamber to enable said gaseous arsine (AsH₃) to communicatewith said ionization chamber; and ionizing said arsine (AsH₃) gas insaid ionization chamber.
 27. The method as recited in claim 26, whereinsaid ionizing step comprises irradiation within said ionization chamberby one or more electron beams.
 28. The method as recited in claim 26,further including the step of controlling the temperature of saidionization chamber to a predetermined value.
 29. The method as recitedin claim 26, wherein said implanting step includes the step ofextracting said dopant cluster ions from said ionization chamber by anelectric field.
 30. The method as cited in claim 29, further includingthe step of mass analyzing the extracted ions and selecting theAs₃H_(x)+ species.
 31. The method as recited in claim 23, furtherincluding the step of: generating P-type dopant cluster ions, andimplanting said P-type dopant cluster ions into said substrate into asecond region different than said first region.
 32. The method asrecited in claim 31, wherein said generating step comprises generatingnegative decaborane cluster ion (B₁₀H_(x) ⁻), where x is an integer and0≦x≦14.
 33. A method of implanting dopant materials into a semiconductorsubstrate comprising: generating N-type dopant cluster ions P₄+; andimplanting said N-type P₄+ dopant cluster ions into a first region ofsaid substrate resulting in N-type doping of said substrate.
 34. Themethod as recited in claim 33, wherein said generating step comprises:providing a source of phosphine (PH₃) gas; providing a conduit betweensaid source of phosphine (PH₃) gas and an ionization chamber to enablesaid gaseous phosphine (PH₃) to communicate with said ionizationchamber; and ionizing said phosphine (PH₃) gas in said ionizationchamber.
 35. The method as recited in claim 34, wherein said ionizingstep comprises irradiation within said ionization chamber by one or moreelectron beams.
 36. The method as recited in claim 34, further includingthe step of controlling the temperature of said ionization chamber to apredetermined value.
 37. The method as recited in claim 34, wherein saidimplanting step includes the step of extracting P₄+ ions from saidionization chamber by an electric field.
 38. The method as cited inclaim 37, further including the step of mass analyzing the extractedions by selecting the P₄+ species.
 39. The method as recited in claim33, further including the step of: generating P-type dopant clusterions; and implanting said P-type dopant cluster ions into said substrateinto a second region different than said first region.
 40. The method asrecited in claim 39, wherein said generating step comprises generatingnegative decaborane cluster ions (B₁₀H_(x) ⁻), where x is an integer and0≦x≦14.
 41. A method of implanting dopant materials into a semiconductorsubstrate comprising: generating N-type dopant cluster ions P₃+; andimplanting said N-type P₃+ dopant cluster ions into a first region ofsaid substrate resulting in N-type doping of said substrate.
 42. Themethod as recited in claim 41, wherein said generating step comprises:providing a source of phosphine (PH₃) gas; providing a conduit betweensaid source of phospine (PH₃) gas and an ionization chamber to enablesaid gaseous phosphine (PH₃) to communicate with said ionizationchamber; and ionizing said phosphine (PH₃) gas in said ionizationchamber.
 43. The method as recited in claim 42, wherein said ionizingstep comprises irradiation within said ionization chamber by one or moreelectron beams.
 44. The method as recited in claim 47, further includingthe step of controlling the temperature of said ionization chamber to apredetermined value.
 45. The method as recited in claim 42, wherein saidimplanting step includes the step of extracting P₃+ ions from saidionization chamber.
 46. The method as cited in claim 50, furtherincluding the step of mass analyzing the extracted ions by selecting theP₃+ species.
 47. The method as recited in claim 42 further including thestep of: generating P-type dopant cluster ions; and implanting saidP-type dopant cluster ions into said substrate into a second regiondifferent than said first region.
 48. The method as recited in claim 47,wherein said generating step comprises generating negative decaboranecluster ions (B₁₀H_(x) ⁻), where x is an integer and 0≦x≦14.
 49. Amethod of implanting dopant materials into a semiconductor substratecomprising: generating N-type dopant cluster ions P₂+; and implantingsaid N-type P₂+ dopant cluster ions into a first region of saidsubstrate resulting in N-type doping of said substrate.
 50. The methodas recited in claim 49, wherein said generating step comprises:providing a source of phosphine (PH₃) gas; providing a conduit betweensaid source of phosphine (PH₃) gas and an ionization chamber to enablesaid gaseous phosphine (PH₃) to communicate with said ionizationchamber; and ionizing said phosphine (PH₃) gas in said ionizationchamber.
 51. The method as recited in claim 50, wherein said ionizingstep comprises irradiation within said ionization chamber by one or moreelectron beams.
 52. The method as recited in claim 50, further includingthe step of controlling the temperature of said ionization chamber to apredetermined value.
 53. The method as recited in claim 50, wherein saidimplanting step includes the step of extracting P₂+ ions from saidionization chamber by an electric field.
 54. The method as recited inclaim 50, further including the step of mass analyzing the extractedions by selecting the P₂+ species.
 55. The method as recited in claim50, further including the step of: generating P-type dopant clusterions; and implanting said P-type dopant cluster ions into said substrateinto a second region different than said first region.
 56. The method asrecited in claim 55, wherein said generating step comprises generatingnegative decaborane cluster ion (B₁₀H_(x) ⁻), where x is an integer and0≦x≦14.
 57. A method of implanting dopant materials into a semiconductorsubstrate comprising: generating N-type cluster dopant ions P₄H_(x)+,where x is an integer and 1≦x≦6; and implanting said N-type P₄H_(x)+dopant cluster ions into a first region of said substrate resulting inN-type doping of said substrate.
 58. The method as recited in claim 57,wherein said generating step comprises: providing a source of phosphine(PH₃) gas; providing a conduit between said source of phosphine (PH₃)gas and an ionization chamber to enable said gaseous phosphine (PH₃) tocommunicate with said ionization chamber; and ionizing said phosphine(PH₃) gas in said ionization chamber.
 59. The method as recited in claim58, wherein said ionizing step comprises irradiation within saidionization chamber by one or more electron beams.
 60. The method asrecited in claim 58, further including the step of controlling thetemperature of said ionization chamber to a predetermined value.
 61. Themethod as recited in claim 58, wherein said implanting step includes thestep of extracting P₄H_(x)+ ions from said ionization chamber by anelectric field, where x is an integer and 1≦x≦6.
 62. The method as citedin claim 61, further including the step of mass analyzing the extractedions by selecting said dopant cluster ions.
 63. The method as recited inclaim 57, further including the step of: generating P-type dopantcluster ions; and implanting said P-type dopant cluster ions into saidsubstrate into a second region different than said first region.
 64. Themethod as recited in claim 63, wherein said generating step comprisesgenerating negative decaborane cluster ions (B₁₀H_(x) ⁻), where x is aninteger and 0≦x≦14.
 65. A method of implanting dopant materials into asemiconductor substrate comprising: generating N-type cluster dopantions P₃H_(x)+, where x is an integer and 1≦x≦5; and implanting saidN-type P₃H_(x)+ dopant cluster ions into a first region of saidsubstrate resulting in N-type doping of said substrate.
 66. The methodas recited in claim 65, wherein said generating step comprises:providing a source of phosphine (PH₃) gas; providing a conduit betweensaid source of phosphine (PH₃) gas and an ionization chamber to enablesaid gaseous phosphine (PH₃) to communicate with said ionizationchamber; and ionizing said phosphine (PH₃) gas in said ionizationchamber.
 67. The method as recited in claim 66, wherein said ionizingstep comprises irradiation within said ionization chamber by one or moreelectron beams.
 68. The method as recited in claim 66, further includingthe step of controlling the temperature of said ionization chamber to apredetermined value.
 69. The method as recited in claim 66, wherein saidimplanting step includes the step of extracting said dopant cluster ionsfrom said ionization chamber by an electric field.
 70. The method ascited in claim 66, further including the step of mass analyzing theextracted ions and selecting said dopant cluster ions.
 71. The method asrecited in claim 65, further including the step of: generating P-typedopant cluster ions; and implanting said P-type dopant cluster ions intosaid substrate into a second region different than said first region.72. The method as recited in claim 71, wherein said generating stepcomprises generating negative decaborane cluster ions (B₁₀H_(x) ⁻),where x is an integer and 0≦x≦14.
 73. A method of implanting dopantmaterials into a semiconductor substrate comprising: generating anN-type cluster dopant ions P₂H_(x)+, where x is an integer and 1≦x≦4 andimplanting said N-type P₂H_(x)+, dopant cluster ions into a first regionof said substrate resulting in N-type doping of said substrate.
 74. Themethod as recited in claim 73, wherein said generating step comprises:providing a source of phosphine (PH₃) gas; providing a conduit betweensaid source of phosphine (PH₃) gas and said ionization chamber to enablesaid gaseous phosphine (PH₃) to communicate with said ionizationchamber; and ionizing said phosphine (PH₃) gas in said ionizationchamber.
 75. The method as recited in claim 73, wherein said ionizingstep comprises irradiation within said ionization chamber by one or moreelectron beams.
 76. The method as recited in claim 73, further includingthe step of controlling the temperature of said ionization chamber to apredetermined value.
 77. The method as recited in claim 73, wherein saidimplanting step includes the step of extracting said dopant ions fromsaid ionization chamber by an electric field.
 78. The method as cited inclaim 77, further including the step of mass analyzing the extractedcluster ions and selecting the P₂H_(x)+ species, where x is an integerand 1≦x≦4.
 79. The method as recited in claim 73, further including thestep of: generating P-type dopant cluster ions; and implanting saidP-type dopant cluster ions into said substrate into a second regiondifferent than said first region.
 80. The method as recited in claim 79,wherein said generating step comprises generating negative decaboranecluster ions (B₁₀H_(x) ⁻), where x is an integer and 0≦x≦14.
 81. Amethod of implanting a cluster ion dopant material into a semiconductorsubstrate comprising the steps of: generating a dopant ion cluster,B_(n)H_(x)+, where n and x are integers and 2≦n≦9 and 0≦x≦14; andimplanting said dopant ion cluster into a first region of saidsubstrate.
 82. The method as recited in claim 81, wherein saidgenerating step comprises: providing a source of diborone (B₂H₆) gas;providing a conduit between said source of diborone (B₂H₆) gas and anionization chamber to enable said diborone (B₂H₆) gas to communicatewith said ionization chamber; and ionizing said diborone (B₂H₆) gas insaid ionization chamber.
 83. The method as recited in claim 82, whereinsaid ionizing step comprises irradiation within said ionization chamberby one or more electron beams.
 84. The method as recited in claim 82,further including the step of controlling the temperature of saidionization chamber to a predetermined value.
 85. The method as recitedin claim 82, wherein said implanting step includes the step ofextracting said dopant cluster ions from said ionization chamber by anelectric field
 86. The method as cited in claim 95, further includingthe step of mass analyzing the extracted ions by selecting said dopantcluster ions.
 87. The method as recited in claim 81, further includingthe step of: generating P-type dopant cluster ions; and implanting saidP-type dopant cluster ions into said substrate into a second regiondifferent than said first region.
 88. The method as recited in claim 87,wherein said generating step comprises generating negative decaboranecluster ions (B₁₀H_(x) ⁻) where x is an integer and 0≦x≦14.
 89. A methodof implanting dopant materials into a semiconductor substratecomprising: generating P-type negative decaborane cluster dopant ions(B₁₀H_(x) ⁻), where x is an integer and 0≦x≦14; and implanting saidnegative decaborane (B₁₀H_(x) ⁻) dopant cluster ions into a first regionon said substrate resulting in P-type doping of said substrate.
 90. Themethod as recited in claim 88, wherein said generating step comprises:providing a source of decaborane (B₁₀H₁₄) vapor; providing a conduitbetween said source of decaborane (B₁₀H₁₄) vapor and an ionizationchamber to enable said decaborane (B₁₀H₁₄) vapor to communicate withsaid ionization chamber; and ionizing said decaborane (B₁₀H₁₄) vapor insaid ionization chamber.
 91. The method as recited in claim 90, whereinsaid ionizing step comprises irradiation within said ionization chamberby one or more electron beams.
 92. The method as recited in claim 90,wherein further including the step of controlling the temperature ofsaid ionization chamber to a predetermined value.
 93. The method asrecited in claim 90, wherein said implanting step includes the step ofextracting negative decaborane cluster ions B₁₀H_(x) ⁻ from saidionization chamber, where x is an integer and 0≦x≦14.
 94. The method asrecited in claim 93, further including the step of mass analyzingnegative decaborane cluster ions B₁₀H_(x) ⁻, species where x equals0≦x≦14.
 95. A semiconductor device comprising: a substrate having one ormore N-type regions formed from an N-type material; and a P-type dopantimplanted into said N-type region, said P-type dopant formed byimplantation of negative decaborane cluster ions B₁₀H_(x) ⁻ into saidp-type region, where x is an integer and 0≦x≦14.
 96. The method asrecited in claim 8, wherein said generating step comprises generatingpositive decaborane (B₁₀H_(x)+) cluster ions, where 0≦x≦14.
 97. Themethod as recited in claim 17, wherein said generating step comprisesgenerating positive decaborane (B₁₀H_(x)+) cluster ions, where 0≦x≦14.98. The method as recited in claim 26, wherein said generating stepcomprises generating positive decaborane (B₁₀H_(x)+) cluster ions, where0≦x≦14.
 99. The method as recited in claim 35, wherein said generatingstep comprises generating positive decaborane (B₁₀H_(x)+) cluster ions,where 0≦x≦14.
 100. The method as recited in claim 44, wherein saidgenerating step comprises generating positive decaborane (B₁₀H_(x)+)cluster ions, where 0≦x≦14.
 101. The method as recited in claim 53,wherein said generating step comprises generating positive decaborane(B₁₀H_(x)+) cluster ions, where 0≦x≦14.
 102. The method as recited inclaim 62, wherein said generating step comprises generating positivedecaborane (B₁₀H_(x)+) cluster ions, where 0≦x≦14.
 103. The method asrecited in claim 71, wherein said generating step comprises generatingpositive decaborane (B₁₀H_(x)+) cluster ions, where 0≦x≦14.
 104. Themethod as recited in claim 80, wherein said generating step comprisesgenerating positive decaborane (B₁₀H_(x)+) cluster ions, where 0≦x≦14.105. The method as recited in claim 89, wherein said generating stepcomprises generating positive decaborane (B₁₀H_(x)+) cluster ions, where0≦x≦14.
 106. The method as recited in claim 98, wherein said generatingstep comprises generating positive decaborane (B₁₀H_(x)+) cluster ions,where 0≦x≦14.
 107. A method of forming cluster ions comprising:providing a supply of dopant atoms into an ionization chamber; andcombining the dopant atoms into clusters containing a plurality ofdopant atoms.
 108. The method as recited in claim 107 furthercomprising: ionizing the dopant clusters into dopant cluster ions;extracting said dopant cluster ions; and implanting said dopant clusterions into a substrate.
 109. The method as recited in claim 107, whereinsaid supply of dopant atoms is in the form of A_(s)H₃.
 110. The methodas recited in claim 109, wherein said supply of dopant atoms is in theform of PH₃.
 111. The method as recited in claim 109, wherein saidsupply of dopant atoms is in the form of B₂H₆.
 112. A method of formingcluster ions comprising: providing a supply of dopant molecules into anionization chamber; and combining the dopant molecules into clusterscontaining a plurality of dopant molecules.
 113. The method as recitedin claim 112 further comprising: ionizing the dopant clusters intodopant cluster ions; extracting said dopant cluster ions; and implantingsaid dopant cluster ions into a substrate.
 114. The method as recited inclaim 113, wherein said supply of dopant atoms is in the form ofA_(s)H₃.
 115. The method as recited in claim 113, wherein said supply ofdopant atoms is in the form of PH₃.
 116. The method as recited in claim113, wherein said supply of dopant atoms is in the form of B₂H₆. 117.The method as recited in claim 81, wherein said generating stepcomprises: providing a source of decaborane (B₁₀H₁₄) vapor; providing aconduit between said source of decaborane (B₁₀H₁₄) vapor and anionization chamber to enable said gas to communicate with saidionization chamber; and ionizing said decaborane (B₁₀H₁₄) vapor in saidionization chamber.